This invention relates to valves for puncturing and releasing gas from pressurized cylinders.
Numerous configurations for valves of this type are known. U.S. Pat. Nos. 805,474, 1,782,020, 1,826,088, 2,028,651 2,634,754, 3,070,818, 3,633,596, 3,938,704 and 4,463,929 illustrate some of the designs which have been proposed.
Although many prior art valves work successfully with low pressure cylinders e.g., cylinder whose internal pressures are on the order of 800 pounds per square inch (psi), such valves are generally not adaptable for use with high pressure cylinders, e.g., cylinders whose internal pressures are on the order of 6,000 psi. Specifically, it takes more force to break the seal on a high pressure cylinder than it does on a low pressure cylinder. Accordingly, it has generally been found difficult to break these seals with existing low pressure puncturing mechanisms and, in particular, with manually-operated mechanisms, including manually-operated mechanisms employing cam and springs to aid the user in puncturing the seal.
Moreover, the breaking of the seal on a high pressure cylinder produces an exiting stream of high pressure gas. This escaping gas represents an additional force which the puncturing mechanism must overcome to open the cylinder. In general, it has been found difficult to generate enough inward force to quickly and reliably open the seal on high pressure cylinders in the presence of escaping gas with existing low pressure puncturing mechanisms and, in particular, manually-operated mechanisms.
High pressure cylinders filled with nitrogen or air and employing poppet type valves have been used to inflate life rafts. However, because of the problems discussed above, cylinders employing puncture type seals and, in particular, hermetically sealed cylinders, have not been used with these gases at high pressures. Rather, these types of seals have been limited to low pressure cylinders employing carbon dioxide as the primary inflation gas. As is recognized in the art, puncture type seals and, in particular, puncture type seals in which the cylinder is hermetically sealed, are preferred to poppet type seals because of the reduced chance of significant loss of pressure during storage.
The inflation of life rafts would benefit from the availability of a reliable valve for high pressure cylinders employing puncture type seals since this would mean that these cylinders could be used when nitrogen or air, instead of carbon dioxide, is to be the primary inflation gas. Although carbon dioxide is a suitable gas for inflating life rafts at normal temperatures, problems develop when either low or high temperatures are encountered, e.g., low temperatures on the order of -30.degree. F. or high temperatures on the order of +150.degree. F. Such temperatures can be encountered for life rafts used in aircraft, especially when the life raft is stored in the aircraft's wings.
At low temperatures, the liquid carbon dioxide in the cylinder vaporizes slowly resulting in a slow inflation process. Moreover, the expansion of the carbon dioxide vapor as it passes out of the cylinder into the life raft results in even lower temperatures which causes the carbon dioxide vapor to solidify into dry ice. The dry ice, in turn, can block the exit passages in the valve, thus further slowing the inflation process, and can accumulate on and thus damage the fabric making up the life raft. At high temperatures, on the other hand, the pressure in the cylinder can increase to levels characteristic of a high pressure cylinder thus bringing into play the problems, discussed above, which arise in puncturing high pressure cylinders.
In contrast, nitrogen and air do not exhibit temperature dependent problems over the -30.degree. F. to +150.degree. F. range, or, for that matter, even substantially beyond that range. Indeed, charges of nitrogen have been included in carbon dioxide cylinders to help propel liquid carbon dioxide out of the cylinder under low temperature conditions. However, to provide the same number of cubic feet of gas at one atmosphere pressure from a cylinder filled with nitrogen or air as are provided by a cylinder filled with liquid carbon dioxide, pressures on the order of 6,000 psi must be employed. To date, notwithstanding their superior properties in comparison to carbon dioxide, this need for higher pressures and the resulting need for a reliable valve capable of puncturing high pressure cylinders have prevented the use of puncture-type nitrogen or air cylinders in the inflation of life rafts.